Electron discharge device employing cavity resonators



Nov. 15, 1949 D. 0. NORTH ELECTRON DISCHARGE DEVICE! EMPLOYING CAVITY RESONATORS 3 Sheets-Sheet 1 Original Filed June 30, 1945 INVENTOR' DuneHT 0. NORTH BY I g V (71/ ATTORN I Nov. 15, 1949 D. 0. NORTH ELECTRON DISCHARGE DEVICE EMPLOYING CAVITY RESONATORS 5 Sheets-Sheet 2 Original Filed June 50, 1943 INVEN'TOR Dunsa-rr 0. NO TH 0W ATTORN Nov. 15, 1949 D. 0. NORTH ELECTRON DISCHARGE DEVICE EMPLOYING CAVITY RESONATORS 3 Sheets-Sheet 3 Original Filed June 30, 1945 INVEYNTOR Dw IGHT 0. NORTH TORNE .one-half the period of the resonator.

Patented Nov. 15, 1949 ELECTRON DISCHARGE DEVICE EM- PLOYING CAVITY RESONATORS Dwight 0. North, Cranbury, N. J., assignor 'to Radio Corporation of America, a corporation of Delaware Original application June 30, 1943, Serial No. 492,818. Divided and this application February 28, 1946, Serial No. 650,799

11 Claims.

My invention relates to electron discharge devices useful at ultra high frequencies and more particularly to such devices utilizing electron beams directed through cavity resonators.

Thepresent application is a division of my copending application Serial No. 492,818 filed June 30, 1943, now Patent 2,413,244, issued December 24, 1946, and assigned to the same assignee as the present application. 7 In electron discharge devices utilized for ultra high frequency operation the problem of noise is serious and in the design of such devices a chief concern is the provision of large signal-to-noise ratio; that is, a low noise factor.

The use of hollow conducting bodies or cavity resonators in combination with electron discharge devices when used at ultra high frequencies has become common practice due to the peculiarly suitable characteristics of these cavity resonators at these high frequencies. A cavity resonator may be electrically excited by means of the passage of a beam of electrons through the resonator. Variations in current density of the electron beam will induce currents and hence electric fields within the resonator corresponding to the variafirst place due to noise caused by shot effects within the electron beam, this noise thereby becomes augmented in the output of the tube.

It has also been suggested that the resonator be used for deflecting a beam passing through the resonator. The requirements for maximum deflection sensitivity are such that the effects of induced noise as described are likely to be the greatest when maximum deflection sensitivity is provided for, that is, when the transit time of the electron through the resonator is equal to about These noise voltages which are amplified within the resonator may cause a significant and sometimes major portion of the total noise produced by the entire receiving system. 7

It is, therefore, an object of my invention to provide an electron discharge device useful at ultra high frequencies in which the signal-tonoise ratio is high, that is, the noise factor is low.

Another object of my invention is to provide.

an electron discharge device useful at ultra high frequencies and having improved characteristics and utilizing cavity resonators through which a beam of electrons may be directed.

More specifically it is an object of my invention to provide an electron discharge device of the beam deflection type useful at ultra high frequencies and employing cavity resonators but in which the induced input noise is eliminated or reduced to a negligible value.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the inven-' tion itself will best be understood by reference to the following description taken in connection with the accompanying drawings in which Figure 1 is a schematic diagram illustrating the principles of my invention; Figure 2 is a longitudinal section of one form of electron discharge device made according to my invention; Figure 3 is a longitudinal section of Figure 2 taken at with respect to Figure 2; Figure 4 is a longitudinal section of a modification of an electron discharge device made according to my invention; Figure '5 is a longitudinal section taken at 90 with respect to Figure 4; Figure 6 is an enlarged view of the cavity resonator used in the device shown in Figures 4 and 5; Figure 7 is a longitudinal section of a still further modification of an electron discharge device made according to my invention and its associated circuits; Figures 8, 9 and 10 are diagrams illustrating certain principles of operation; and Figure 11 is a schematic diagram of a modified form of cavity resonator which may be utilized in the device shown in Figures 4 and 5.

As pointed out above, the object of the present invention is to provide an electron discharge device employing a cavity resonator which will produce deflection of a beam of electrons traversing it but which will not be excited by pre-existing current density modulation or variation in the beam. Mathematically it can be shown that to meet this requirement the integral IE. (I Z of an electron traversing the cavity must approach zero. In this integral 3 is the vector position of the electron, and E is the oscillating electric field vector which exists at the electron when the cavity resonator is filled with radiation at the operating (resonance) frequency. In order to fulfill the above condition, the electron should be made to move through a region of the cavity resonator in which the field strength 5 is preferably large but essentially. everywhere at right angles to the electron beam.

In Figure 1 is shown a section of a resonator having re-entrant portions II and I2, the resonator surfaces being defined by the surface of revolution of a geometric figure about the axis 0-0. The dotted lines represent theE lines or electron in the plane AA fulfills the condition described above.

For a practical device it is desirable to move the electrons through the central region where E is large. An electron discharge device incorporating a practical form of this type of resonator is disclosed in Figures 2 and 3. An indirectly heated cathode N5 of the type employed for generating an electron beam has mountedadjacent to it an electrode H for defining the beam and directing it through the resonator to an apertured electrode l8' and a collector l9. The rod'lt' may bisect the aperture in electrode I8 to provide a double aperture to obtain certain desired output characteristics. g

The resonator. is of the'form shown in Figure 1 and has re-entrant portions 2l and 22, the inner surfaces of which are oppositely disposed and lie in parallel planes parallel to the path of the beam between the cathode and collector. In order to introduce the beam between these surfaces and to shield the beam from any portion of the field outside of the field between these surfaces, the reentrant conducting members 23 and 24 of tubular form project inwardly of the resonatorand are coaxial with the apertures 2| and 22' in the resonator and through which the beam is directed. These tubular conducting members 23 and 24 extend toward but are spaced from the surfaces of the re-entrant portions 2| and 22.

In operation a beamof electrons is directed from the cathode l6 through the resonator'm'to the collector I9, the beam being subjected to the high frequency alternating electric field between the surfaces of the re-entrant portions 2| and 22, this field being substantially perpendicular to the beam at all times. Theresonator geometry satisfies the conditions set forth that the beam shall pass through the field of the resonator at right angles to the field and that pre-existing current density variations will not induce a voltage within the resonator. The resonatormay be excited from an external source by means of a loop 20" coupled to the field within the resonator 20, the resonator being provided with an aperture through which the re-entrant portion I5 of the envelope extends to permit insertion of the coupling loop 20'.

In Figures 4 and 5 is shown a modification of the device shown in Figures 2 and 3 utilizing a different form of resonator and afslightly different form of collector and targetelectrode system.

As pointed out above, the purpose of the tubular members 23 and 24 in the resonator used in the devices shown in Figures 2 and 3 is to keep .the electrons shielded from all but the most intense part of the electrical field .within the cavity resonator. This is important, for best operation 4 will occur when exposure to the field is no greater than one-half the resonant period. If the tubular members were omitted, control over the exposure time to the field would be lost or substantially so. The purpose of the construction of the resonator shown in Figures 4, 5 and 6 is to still retain the control while eliminating the tubular members, which might under certain conditions adversely affect the oscillating fields within the resonator.

The envelope 25 has mounted within it a preferably indirectly heated cathode 26 and a collector 28. The cavity resonator 3| comprises essentially two hollow conducting bodies 32 and 33 having oppositely disposed spaced parallel sides or walls 32 and 33 provided with centrally positioned apertures 35 and 36'. The portions 32 .and 33 have re-entrant portions 35 and 36 extended to and through the apertures 35 and 36 so as to provide oppositely disposed parallel surfaces between which a beam of electrons may be directed. A conducting collar 34 is coaxial with the apertures in the walls 32' and 33' and en closes the space between the apertures and provides a communicating passageway between the interiors of said hollow conducting bodies 32 and 33. The collar member 34 is provided withop' positely disposed apertures 31 and 38 which reg ister with the space between the parallel surfaces of the re-entrant portions 35 and 36. Thus the electron beam is shielded from the fields within the resonator except for the field between the opposed surfaces of the re-entrant portions 35 and 36. The annular depression in the resonator, provided by the walls 32' and 3 3 and the collar 34 in Figures 4-6, not only shields the beam but also makes the field distribution within the resonator more uniform around the portions 35 and 36. One of the hollow conducting bodies 32 and 33 may be provided with an aperture 33" into which the re-entrant portion 25' of the envelope extends to permit the insertion of the coupling loop 3|. As shown the cathode 26 and collector 28 are mounted within the annular depression between the two halves of the resonator and close to the apertures 3! and 38.. This arrangement permits shortening of the overall length of the beam, which lightens the focusing difliculties due to a long beam.

The various voltage sources for the cathode and the resonator 3| are shown at 39 and 4|, and the output circuit 42 is connected to the collector 28. Another modification of my invention is shown in Figure 7. The envelope 45 has mounted at one end an indirectly heated cathode 46 and a beam forming electrode 41,- and at the other end a collector 48, a secondary emission suppressor electrode 49 and an apertured electrode 50 across which the beam may be deflected. Mounted within the envelope are a pair of truncated coneshaped members 5| and 52, the smaller diameter ends being opposite to each other and being closed by surfaces lying in parallel planes. Surrounding these cone-shaped members is a hollow drum-shaped member comprising other truncated cone-shaped elements 53 and 54 connected by means to a collar member provided with oppositely disposed beam apertures 56 and 51 registering with the space between the parallel surfaces of the cone-shaped members 52 and 5|.

The cone-shaped elements'5l, 52, 53 and 54 provide a surface of revolution of a geometrical figure including a pair of opposed substantially trapezoidal figures about and spaced from an axis of revolution transverse to the path of the electron beam. These cone-shaped members are provided with leads and supports in the form of collars or rings 52', 5|, 53' and 54' extending through the glass envelope. There may be mounted between the beam forming electrode 41 and the cone-shaped members 53 and 54 a tubular member 58 provided with an apertured partition 58, the aperture 58" registering with the apertures 5! and 56 in the collar member 55. To complete the resonator I provide the hollow conducting bodies 59 and 60 formed by a surface of revolution of a geometric figure so as to provide extensions for the cone-shaped bodies 52, 54, 53 and 5|, these members being provided with spring fingers such a-s59', 59", 60 and 60" which engage the collar-like extensions 52', 54', 5| and 53', these hollow conducting bodies 59 and 60 being held in contact by means of bolts 6! and 62 screwed into cup-shaped elements 65 and 66 secured to the bodies 52 and 5i. With the members 59 and 60 removable, different sizes can be used for different frequencies.

It will be observed that in Figure 7 I have in effect provided a cavity resonator symmetrical about an axis passing through the bolt members BI and 52, the re-entrant cone-like members providing surfaces between which the electric field is generated to deflect the electron beam.

A coupling loop may be inserted within the resonator to excite the same. The voltage sources are shown at B1, 68 and 69. The output circuit H is connected to the collector or anode 48. The interior of the hollow bodies may be silver plated to reduce surface resistance and losses due to this resistance.

In connection with the forms of resonator so far described and particularly with reference to the form of resonator utilized in Figures 4, 5 and 6, to facilitate the establishment of the proper dynamic state when only one-half of the resonator is excited, a modification may be provided. To illustrate the problem of excitation reference may be had to Figures 8 to 10, inclusive.

In Figure 10 are illustrated schematically two identical concentric line resonators back to back. They comprise the outer tubular member and the inner conductors 16 and TI closed at their ends at 18 and 19. The partition 80 separates the two resonators. If each resonator is now separately excited to produce the fields shown by the arrow lines, the partition plane 80 serves no purpose, for if it were removed, the if lines of the fields would join. It is, therefore, believed that having established such a state and having removed the partition, the excitation with one of the excitors removed would be maintained in the two resonators. It is this mode of operation which is necessary for the successful functioning of the device disclosed. On the other hand, suppose that the phase of one of the excitors is reversed. The resulting fields are shown in Figure 8. Here the partition 80 is important and if removed the state illustrated in Figure 9 would result.

The mode of operation illustrated in Figure 9 would not provide a field transverse to an electron beam passing through the center of the resonator in a plane transverse to the coaxial lines. This mode would, therefore, be an undesired mode. This undesired mode will have a higher resonant frequency than the desired mode. If the higher resonant frequency is sufficiently removed from the frequency of the desired mode..so that it falls outside of the signal pass band, no problem is presented. If the higher frequency does not fall outside the signal pass band, the arrange ment shown'in Figure 11 illustrates a cure which makes the undesired mode non-existent; that is, the cavity will simply not resonate in the undesired mode.

If, therefore, difficulty should be experienced with some forms. of device utilizing the cavity resonator shown in Figures 4, 5 and 6, the difficulty might be removed by utilizing the structure illustrated in Figure 11. The resonator 8f comprises the two hollow conducting bodies 82 and 83 and collar member 84 corresponding to the elements 32, 33 and 34 of Figure 6. To insure the type of operation desired and illustrated in Figure 10, a coupling neck or conductor 85 could be extended between the two portions 82 and B3 to provide a communicating passageway so that the field formation will be that as shown in Figure 11, thus stabilizing the mode of operation desired. The undesired mode is nonexistent in this form of resonator, that is, the resonator will not resonate in the undesired manner.

While I have indicated the preferred embodiments of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it will be apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims.

What I claim as new is:

1. An electron discharge device having a cathode for supplying a beam of electrons and a collector for receiving said electrons and a cavity resonator positioned between the cathode and the collector, said cavity resonator comprising a hollow drumshaped member, the ends of said member being provided with re-entrant portions extending toward one another, a said reentrant portions providing surfaces within the resonator lying in planes parallel to one another,

the space between the surfaces lying in parallel planes, the beam path extending through said apertures.

2. An electron discharge device having a cathode for supplying a beam of electrons and a collector for receiving said electrons, and a cavity resonator positioned between the cathode and the collector, said cavity resonator comprising a hollow drum-shaped member, the end walls of said member having re-entrant portions extending toward one another, said re-entrant portions providing surfaces within the resonator lying in planes parallel to one another and to the beam path, the surface of said member extending between said end walls being provided with an annular depression, the annular depression having apertures in opposite walls of the resonator registering with the space between the surfaces lying in parallel planes, the beam path passing through said apertures.

3. An electron discharge device having a .cathode for supplying a beam of electronsand a collector for receivingsaid electrons andwa cavity resonator positioned between the cathode and the collector, said cavity resonator .comprisinga hollowpdrum-shaped -member,.,the endwalls of said memberbeing provided with'reeentrant portions extending 'towardone another, said re.-entrant portions providing surfaces within the resonator lying, .in planes parallel toone another, the surface :of said member extending betweenthe end Walls being provided with an annular depression having a. substantially V.-shaped transverse section, said depression having oppositely. disposed apertures in thewalls of said resonator register-9 ing with the space between the surfaces lying in planes parallel to one another and with said cathode and collector;

4. An electron discharge device having an envelope, cathode means in] said envelope for providing a beam of electrons, a. collector in said envelope for receiving said electrons and means positioned between the cathode means and collector and comprising a pair of re-entrant truncated cone-shapedmembersthe truncated 'apices of which provide oppositely disposed surfaces lying in planes parallel to the beam pathand between which the beam path extends, a hollow drum-shaped member surrounding said cone shaped members and having a surface conforming substantially to theysurfaces of said coneshaped members but spaced-therefrom, said coneshaped members and said drum-shaped member bers contacting said conducting lips and'communicating with the space between the. coneshaped members and the drum-shaped member for providing a cavity resonator, the, drumshaped member being provided with oppositely disposed apertures registering with the space between the truncated apices of said coneshaped members and through whichthe'beam path extends.

5. An electron discharge device having an. en? velope and cathode means in' said envelope for providing a beam of electrons, a collector in said envelope for receiving said electrons and means positioned between the cathodemeans and collector and comprising a pair of reeentrant truncated cone-shaped members, the truncated apices of which provide oppositely, disposed surfaces lying in planes parallel toxthe. beam'path and between which the beam path extends, va hollow drum-shaped member surrounding said coneshaped members and having a surfaceconforming substantially to the surfaces of said cone-shaped members but spaced therefrom, said cone-shaped members and said drum-shaped member having conducting elements extending through the envelope, said conducting elements comprisinga plurality of concentric ring-like members, and hollow conductingmembers contacting said ring.- like members and communicating withthespace between the cone-shaped members andthe drumshaped member for providing a. cavity resonator, the drum-shaped member being. provided'with registering apertures through which the beam path extends.

6. An electron discharge device having. a cathode for supplying a stream of electrons and a collector for receiving :said electrons and a cavity resonator positionedbetween the cathode and the collector, the path of said stream of electrons extending through said resonator, .said

resonator comprisingasurfaceof revolution of-a i geometric figure including a pair of opposed elongated substantially trapezoidal figures, said trapezoidal figures being spaced from the axis of revolution, said axis of revolution being. transverse to the path of the electron stream, said resonator being provided with a' pair ofoppositely disposed apertures through which the path of the electron stream extends, said resonator having surfaces within the resonator lying in parallel planesand between which the path of the stream of electronslies.

7; An electron discharge device having a cath-' ode'means for supplying a directed beam of electrons and a collector for receiving said electrons and a cavity resonator positioned between the cathode means and collector, said resonator comprising a pair of like hollow conducting members spaced from each other and having registering aperturesinadjacent walls, each of said hollow conducting members having a re-entrant portion extending toward the aperture and having a. surface lying in a plane, said surfaces being parallel and oppositely disposed, the beam path lying parallel to and between said surfaces, and a conducting member extending between said hollow conducting members and coaxial with said apertures and enclosing the space between said apertures, said last conducting member being pro.- vided with oppositely disposed apertures through which the beam path extends.

8. An electron discharge device having a cathode means for supplying a directed beam of elec+ trons and a collector for receiving said electrons and a cavity resonator positioned between the cathode means and collector, said resonator comprising a pair of like hollow conducting members spaced from each other and having spaced oppositely disposed parallel walls having registering apertures in said walls, each of said hollow conducting members having a re-entrant portion extending toward the aperture and having surfaces lying in a plane, said surfaces being oppositely disposed and parallel, the beam path lying parallel to and between said surfaces, and a conducting member extending between said hollow conducting members and coaxial with said apertures, and enclosing the space between said apertures, said last conducting member being provided with oppositely disposed apertures through which the beam path extends.

9'. An electron discharge device having a cathode for supplying a beam'of electrons and a collector for receiving said electrons, and a cavity resonator positioned between the cathode and the collector, said cavity resonator comprising a surface of revolution of :a geometric figure, the exterior of said surface 'of revolution having an annular depression extending around the axis of revolution, the walls of said resonator being reentrant along said axis of revolution to provide oppositely disposed surfaces within the resonator, said resonator having apertures within said annular depression oppositely disposed and registering with each other and the space between said oppositely disposed surfaces, said cathode and collector being positioned adjacent said apertures.

10. An electron discharge device having a cathode for supplying a beam of electrons and a collector for receiving said electrons, and a cavity resonator through which the beam of electrons is directed, said cavity resonator comprising a hollow drum-shaped member, the end walls of saidmember having rte-entrant portions extending toward one another, said re-entrant portions ,-providing-surfaces within the resonator. lying in planes parallel to one another and to the beam path, the surface of said member extending between said end walls having an annular depression, the annular depression having apertures in opposite walls of the resonator registering with the space between the surfaces lying in parallel planes, said cathode and said collector being positioned within said annular depression and adjacent said apertures.

11. An electron discharge device having a cathode for supplying a beam of electrons and a collector for receiving said electrons, and a cavity resonator through which the beam of electrons is directed, said cavity resonator comprising a pair of like hollow conducting members spaced from each other and having registering apertures in adjacent walls, each of said hollow conducting members having a reentrant portion extending toward the aperture and having a surface lying in a plane, said surfaces being parallel and oppositely disposed, the beam path lying parallel to and between said surfaces and a conducting member extending between said pair of like CES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,190,668 Llewellyn Feb. 20, 1940 2,272,165 Varian et a1 Feb. 3, 1942 2,275,480 Varian et al. Mar. 10, 1942 2,320,860 Fremlin June 1, 1943 

